Mercaptosilanes have been known for use in tire applications to couple fillers to the rubber; however their utility in CASE has been limited due to the reactivity of the mercaptan functionality with catalysts which are used in CASE, i.e., the catalysts react with the mercaptan group thus de-activating the catalyst.
Specifically, the prior art discloses acylthioalkyl silanes, such as CH.sub.3 C(.dbd.O)S(CH.sub.2).sub.1-3 Si(OR).sub.3 [M. G. Voronkov et al. in Inst. Org. Khim., Irkutsk, Russia] and HOC(.dbd.O)CH.sub.2 CH.sub.2 C(.dbd.O)S(CH.sub.2).sub.3 Si(OC.sub.2 H.sub.5).sub.3 [U.S. Pat. No. 3,922,436 to R. Bell et al.]. Japanese Patent 63270751A2 and DE 2508931 disclose the use of compounds represented by the general formula, CH.sub.2.dbd.C(CH.sub.3)C(.dbd.O)S(CH.sub.2).sub.1-6 Si(OCH.sub.3).sub.3 in tire tread compositions, and adhesive compositions, respectively, but these compounds are not desirable because the unsaturation .alpha.,.beta. to the carbonyl group of the thioester has the undesirable potential to polymerize during the compounding process, during storage or during the service life of the adhesive or coating.
Prior art by Yves Bomal and Olivier Durel, in Australian Patent AU-A-10082/97, discloses the use in rubber in conjunction with functionalized siloxanes of silanes of the structure represented by R.sup.1.sub.n X.sub.3-n Si--(Alk).sub.m (Ar).sub.p --S(C.dbd.O)--R where R.sup.1 is phenyl or alkyl; X is halogen, alkoxy, cycloalkoxy, acyloxy, or OH; Alk is alkyl; Ar is aryl; R is alkyl, alkenyl, or aryl; n is 0 to 2; and m and p are each 0 or 1, but not both zero.
U.S. Pat. No. 3,922,436 to Bell disclose a mercaptan/acid anhydride adduct as coupling agents for filled plastics, but there is no teaching to de-block the mercaptan group. U.S. Pat. No. 4,820,751 discloses certain blocked mercaptosilane for tires but again does not disclose any de-blocking of such silanes. U.S. Pat. No. 4,519,430 to Ahamd et al. and U.S. Pat. No. 4,184,998 to Shippy et al. disclose the blocking of a mercaptosilane with an isocyanate to form a solid which is added to a tire composition, which mercaptan reacts into the tire during heating, which could happen at any time during processing since this a thermal mechanism.
There remains a need for effective latent coupling agents which exhibit the advantages of mercaptosilanes without exhibiting the disadvantages such as described herein.